PLATELET-RICH PLASMA PROVIDES NUCLEUS FOR MINERALIZATION IN CULTURES OF PARTIALLY DIFFERENTIATED PERIODONTAL LIGAMENT CELLS

Platelet-rich plasma stimulated proliferation, migration, and attachment of cultured periodontal ligament cells

Objective:

The aim of this study is to evaluate the effects of platelet-rich plasma (PRP) on the proliferation, migration, and attachment of cultured periodontal ligament (PDL) cells.

Materials and Methods:

3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to assess number of PDL cells cultured in medium with or without PRP. Cell migration toward medium with or without PRP was assessed using the Boyden chamber. Cell attachment was assessed by counting cells on PRP or non-PRP coated dentin specimens. Group differences were analyzed using two-way ANOVA at 0.05 significance level.

Results:

In the MTT and cell migration assay, the number of cells in 5% and 10% PRP-treated groups were significantly higher than that in the non-PRP-treated group (P < 0.05). In the attachment assay, the number of cells on the dentin specimens in 10% PRP-treated group was significantly higher than that in the non-PRP treated group (P < 0.05).

Conclusion:

PRP could stimulate proliferation, migration, and attachment of PDL cells.

Effect of concentrated growth factor on osteoblast cell response

OBJECTIVE

The purpose of this study was to assess the effect of concentrated growth factor (CGF) on osteoblast cell proliferation and differentiation.

METHODS

SaOS-2 osteoblast-like cells were cultured on titanium discs. The disc surfaces in the test group were treated with CGF serum, and those in the control group were left untreated. Cell counts, cell proliferation, and osteocalcin (OCN) levels were evaluated on days 1 and 3, and the alkaline phosphatase (ALP) activity was assessed on days 3, 7, and 14.

RESULTS

The proliferation values were significantly higher in the test group than in the control on days 1 and 3 (P<0.05). ALP activities increased gradually in both groups from day 3 to day 14, but the ALP values were significantly higher in the test group than in the control in all periods (P<0.05). The OCN level on day 1 was significantly higher (P<0.05) in the test group, and no statistically significant difference was found between the two groups on day 3 (P<0.05). A significant decrease was observed in OCN activity on day3 in comparison with day 1 in the control group (P<0.05).

DISCUSSION

The results suggest that CGF can efficiently stimulate the proliferation and differentiation of osteoblast cells, thereby improving the healing process around implants.

Mineralization by mesenchymal stromal cells is variously modulated depending on commercial platelet lysate preparations

BACKGROUND AIMS

Numerous cellular models have been developed to investigate calcification for regenerative medicine applications and for the identification of therapeutic targets in various complications associated with age-related diseases. However, results have often been contradictory due to specific culture conditions, cell type ontogeny and aging status. Human platelet lysate (hPL) has been recently investigated as valuable alternative to fetal bovine serum (FBS) in cell culture and bone regeneration. A parallel comparison of how all these multiple factors may converge to influence mineralization has yet to be reported.

METHODS

To compare mineralization of human mesenchymal cell types known to differ in extracellular matrix calcification potency, bone marrow-derived mesenchymal stromal cells and dermal fibroblasts from neonatal and adult donors, at both low and high passages, were investigated in an ex vivo experimental model by supplementing the osteogenic induction medium with FBS or with hPL. Four commercial hPL preparations were profiled by liquid chromatography/electrospray ionization quadrupole time-of-flight spectrometry, and mineralization was visualized by von Kossa staining and quantified by morphometric evaluations after 9, 14 and 21 days of culture.

RESULTS

Data demonstrate that (i) commercial hPL preparations differ according to mass spectra profiles, (ii) hPL variously influences mineral deposition depending on cell line and possibly on platelet product preparation methods, (iii) donor age modifies mineral deposition in the presence of the same hPL and (iv) reduced in vitro proliferative capacity affects osteogenic induction and response to hPL.

CONCLUSION

Despite the standardized procedures applied to obtain commercial hPL, this study highlights the divergent effects of different preparations and emphasizes the importance of cellular ontology, donor age and cell proliferative capacity to optimize the osteogenic induction capabilities of mesenchymal stromal cells and design more effective cell-based therapeutic protocols.

Fibrinogen Induces RUNX2 Activity and Osteogenic Development from Human Pluripotent Stem Cells

Pluripotent stem cells, both human embryonic stem cells (hESC) and induced pluripotent stem cells (iPSC), provide an important resource to produce specialized cells such as osteogenic cells for therapeutic applications such as repair or replacement of injured, diseased or damaged bone. hESCs and iPSCs can also be used to better define basic cellular and genetic mechanisms that regulate the earliest stages of human bone development. However, current strategies to mediate osteogenic differentiation of hESC and iPSC are typically limited by the use of xenogeneic components such as fetal bovine serum (FBS) that make defining specific agents that mediate human osteogenesis difficult. Runt-related transcription factor 2 (RUNX2) is a key regulator required for osteogenic differentiation. Here, we used a RUNX2-YFP reporter system to characterize the novel ability of fibrinogen to mediate human osteogenic development from hESC and iPSC in defined (serum-free) conditions. These studies demonstrate that fibrinogen mediates significant osteo-induction potential. Specifically, fibrinogen binds to the surface integrin (α9β1) to mediate RUNX2 gene expression through the SMAD1/5/8 signaling pathway. Additional studies characterize the fibrinogen-induced hESC/iPSC-derived osteogenic cells to demonstrate these osteogenic cells retain the capacity to express typical mature osteoblastic markers. Together, these studies define a novel fibrinogen-α9β1-SMAD1/5/8-RUNX2 signaling axis can efficiently induce osteogenic differentiation from hESCs and iPSCs. Stem Cells 2016;34:2079-2089.

Angiogenic and osteogenic potential of platelet-rich plasma and adipose-derived stem cell laden alginate microspheres

Improving vascularization of tissue-engineered bone can advance cell performance in vivo and further promote bone regeneration. How to achieve a functional vascular network within the construct is one of the biggest challenges so far. We hypothesized that a mixture of platelet-rich plasma (PRP) and adipose-derived stem cells (ADSCs) could endue the alginate microspheres with osteogenic and angiogenic potential. In vitro and in vivo studies were performed to investigate the potential of the PRP-ADSC-laden microspheres. Two intriguing observations were made in this study. First, we demonstrated that PRP sustained cell viability and meanwhile promoted cell migration from the interior of alginate microspheres to the surface. This phenomenon indicated that encapsulated cells have the potential to directly and actively participate into the regeneration process. Second, in vivo, a blood vessel network was found within the 10% PRP and 15% PRP-ADSC implants, which was associated with a significant increase in mineralization. It suggested that the PRP-ADSC-laden microspheres did enhance the vascularization and mineralization. In summary, this strategy not only provides a micro-invasive therapy for bone regeneration, but also could be incorporated with other matrices for extended application.

Bone grafts in craniofacial surgery

Reconstruction of cranial and maxillofacial defects is a challenging task. The standard reconstruction method has been bone grafting. In this review, we shall describe the biological principles of bone graft healing, as pertinent to craniofacial reconstruction. Different types and sources of bone grafts will be discussed, as well as new methods of bone defect reconstruction.

Effect of platelet-rich plasma on dental stem cells derived from human impacted third molars

AIM

Platelet-rich plasma (PRP) is fabricated from autologous blood and extensively used to promote soft and hard tissue healing. In the dental field, autologous PRP is widely used combined with dental implant installation and bone graft. This study will evaluate the biologic effect of PRP on the proliferation and the differentiation of human dental stem cells, and find the key cytokines inducing these effects to estimate the clinical feasibility of PRP for dental tissue engineering.

MATERIALS & METHODS

Venous blood was obtained from four individuals and each PRP was fabricated. The human dental stem cells were obtained from the periodontal ligament (PDL) and dental pulp of the surgically extracted human third molars and expanded in vitro. Immunocytochemical staining and flow cytometry with STRO-1 and CD146 confirmed existence of mesenchymal stem cells in the PDL and dental pulp. The effect of PRP on the proliferation of PDL stem cells (PDLSCs) and dental pulp stem cells (DPSCs) was assessed by colony-forming ability measurement, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and bromodeoxyuridine incorporation assay. Alkaline phosphatase activity and calcium deposit were measured to evaluate the mineralization effect of PRP PDLSCs and DPSCs. Alizarin red S staining was used to detect mineral nodules. Odontogenic and osteogenic gene expressions were evaluated in the PRP-treated PDLSCs and DPSCs by real-time quantitative PCR. A protein array was performed to detect the key cytokines that have an important role in the tissue regenerative effect of PRP.

RESULTS

Flow cytometry cell sorting showed that the cells from human PDL and dental pulp contained mesenchymal stem cell populations. Colony-forming ability and cellular proliferation of the dental stem cells were increased at 0.5 and 1% PRP concentration but decreased at 5% concentration. Long-term treatment with 1% PRP enhanced proliferation of the human dental stem cells PDLSCs and DPSCs by 120 h and showed the most significant enhancement at 96 h. PRP also promoted mineralization differentiation of the two kinds of dental stem cells as shown by measurement of alkaline phosphatase activity and calcium deposit under mineralization conditioned media. Increased formation of mineral nodules stained with alizarin red was observed in both PDLSCs and DPSCs after treatment with 1% PRP. Real-time quantitative PCR showed higher odontogenic and osteogenic gene expressions in PRP-treated PDLSCs and DPSCs. RANTES/CCL5 and ICAM-1 were the two key cytokines that were detected in human cytokine array with PRP.

CONCLUSION

The appropriate concentration of the PRP treatment enhanced proliferation and mineralization differentiation of human dental stem cells. RANTES/CCL5 and ICAM-1 might play an important role in PRP-induced tissue regeneration but further study is needed to investigate the whole mechanism.

The effect of platelet-rich plasma in vitro on primary cells: rat osteoblast-like cells and human endothelial cells

The aim of this study was to evaluate the effects of standardized platelet-rich plasma (PRP) concentrates from 10 human donors on cellular behavior. The standardized PRPs used were fivefold average and fivefold maximum baseline values in whole blood. Both these standardized PRPs were characterized by determining platelet numbers and subsequently growth factor concentrations in activated PRPs, called PRP derivatives. Platelet numbers in both types of standardized PRPs were significantly increased compared with whole blood. Further, both PRP derivatives contained significantly higher concentrations of platelet-derived growth factor-AA, platelet-derived growth factor-AB, and transforming growth factor-beta 1. Vascular endothelial growth factor concentrations were significantly elevated in only the most concentrated PRP derivative. Cell culture experiments with osteoblast-like cells showed that both PRP derivatives stimulated cell proliferation without inducing cell differentiation, whereas tube formation in endothelial cell cultures was significantly increased by adding low volume percentages of PRP derivative (2%&#x2013;8%). Consequently, it can be concluded that there is no direct relationship between the number of platelets and the level of growth factors released from these platelets. PRP derivatives have the potency to stimulate angiogenesis dose dependently, while lacking the capacity to induce osteogenic differentiation. Yet, the proliferation of osteoblast-like cells can significantly be enhanced by supplementation of PRP derivatives.

Evaluation by Bone Scintigraphy of Osteogenic Activity of Commercial Bioceramics (Porous β-TCP and HAp Particles) Subcutaneously Implanted in Rats

Osteogenic potential of biomaterials used in bone regenerative therapy has been mainly examined in an animal-implantation study. We have here evaluated the applicability of bone scintigraphy in imaging ectopic bone formation, especially its initial phase, by β-tricalcium phosphate (β-TCP) particles that were implanted in rat dorsal subcutaneous tissues. In implanted osteogenic osteosarcoma cells used as a positive control, osteoid formation was found by histological examination and bone scintigraphy using 99mTc- hydroxymethyl diphosphonate (HMDP) at 2 and 3 weeks post-implantation, respectively, while the microfocuscomputed tomography (μCT) system required further mineralization, which occurred at 4 weeks. Implantation of β-TCP particles alone induced only faint biomineralization inside the particles, which could be microscopically detected by calcein chelation at 2 weeks post-implantation, but not by other histological examinations (e.g., HE staining) or μCT. However, the bone scintigraphy successfully detected this microscopic change at 1 week. Implanted hydroxyapatite (HAp) particles alone used as a negative control did not induce mineralization at microscopic levels, and therefore nothing was detected by either calcein chelation or bone scintigraphy. In conclusion, the bone scintigraphic methodology, although exhibiting less quantitation and resolution, would be applicable as a non-invasive, highly sensitive methodology in detecting the initial, microscopic changes associated with mineralization.

In vitro effects of Choukroun's PRF (platelet-rich fibrin) on human gingival fibroblasts, dermal prekeratinocytes, preadipocytes, and maxillofacial osteoblasts in primary cultures

OBJECTIVES

The objective of this study was to analyze the effects of Choukroun's PRF (platelet-rich fibrin), a leucocyte and platelet concentrate clinically usable as fibrin membrane or clot, on human primary cultures of gingival fibroblasts, dermal prekeratinocytes, preadipocytes, and maxillofacial osteoblasts.

STUDY DESIGN

For the proliferation study, these cells were cultivated with or without a PRF membrane originating from the same donor as for the cells. For osteoblasts and fibroblasts, dose-dependent effect was assessed (using 2 membranes). Cell counts and cytotoxicity tests were performed at 3, 7, 14, and 21 days, and even 28 days for osteoblasts. More osteoblast cultures were prepared in differentiation conditions according to 3 modalities (without PRF, with PRF, with PRF the first day and differentiation medium applied only after the first week of culture). Osteoblast differentiation was analyzed using Von Kossa staining and alkaline phosphatase, DNA and total cell proteins dosage.

RESULTS

PRF induced a significant and continuous stimulation of proliferation in all cell types. It was dose dependent during all the experiment with osteoblasts, but only on day 14 with fibroblasts. Moreover, PRF induced a strong differentiation in the osteoblasts, whatever the culture conditions. The analysis of osteoblast cultures in differentiation conditions with PRF, using light and scanning electron microscopy, revealed a starting mineralization process in the PRF membrane itself after 14 days. Moreover, PRF leucocytes seemed to proliferate and interact with osteoblasts.

CONCLUSIONS

Cultures with PRF are always cocultures with leucocytes. These "chaperone leucocytes" could be the source of differential geographic regulation within the culture and explain the double contradictory effect proliferation/differentiation observed on osteoblasts.

Periodontal ligament cell sheet promotes periodontal regeneration in athymic rats

AIM

The primary goal of periodontal treatment is regeneration of the periodontium. Current theories suggest that the periodontal ligament (PDL) cells have the capacity to participate in restoring connective and mineralized tissues, when appropriately triggered. We evaluated whether human PDL cell sheets could reconstruct periodontal tissue.

MATERIAL AND METHODS

To obtain the cell sheet, human PDL cells were cultured on temperature-responsive culture dishes with or without osteogenic differentiation medium. The cell sheets were transplanted on periodontal fenestration defects of immunodeficient rats. Forty rats were divided in two groups: in one group, cell sheets cultured with control medium were transplanted and in the other, cell sheets cultured with osteogenic differentiation medium were transplanted. The defects were analysed histologically and histomorphologically after healing.

RESULTS

Most of the experimental group exhibited a new cementum-like layer and new attachment of collagen fibres to the layer. Histomorphological analyses indicated significant periodontal regeneration. The control group revealed dense extracellular matrix and fibre formation, but an obvious cementum layer was not observed.

CONCLUSIONS

Transplanted PDL cell sheets cultured with osteogenic differentiation medium induced periodontal regeneration containing an obvious cementum layer and Sharpey's fibres. Thus, the method could be feasible as a new therapeutic approach for periodontal regeneration.

Platelet gel supplementation in long bone nonunions treated by external fixation

OBJECTIVE

The aim of the present study was to evaluate the use of previously frozen, thawed platelet gel supplementation to accelerate the healing of long bone nonunions treated by external fixation.

DESIGN

Prospective case series with historical controls.

SETTING

University Hospital.

PATIENTS

Twenty patients affected by tibial, humeral, or forearm atrophic nonunions were treated by percutaneous stabilization with unilateral external fixators and injection of autologous platelet gel. The healing time was compared to the result obtained in a historical control group treated without platelet gel supplementation.

MAIN OUTCOME MEASUREMENTS

Consolidation rate and radiographic healing time of nonunions in the 2 groups were assessed by independent blinded observers. The nonunion was judged to be healed when bridging callus formation on both radiographic views was observed on at least 3 of 4 cortices.

RESULTS

The healing rate of nonunion was 90% (18/20) in platelet gel cases and 85% (17/20) in controls, respectively (P = 0.633). The mean time until radiographic consolidation in nonunions supplemented with platelet gel (147 +/- 63 days) was not different to the result in the control group (153 +/- 61 days; P = 0.784). Analyzing the mean healing time for separate segments, no differences were noted between study and control group-that is, tibia: 112 +/- 43 and 130 +/- 5 days, respectively (P = 0.382); humerus, 225 +/- 36 and 202 +/- 70 days, respectively (P = 0.530).

CONCLUSION

The present study failed to show the clinical usefulness of isolated percutaneous platelet gel supplementation in long bone nonunions treated by external fixation; however, caution should be exercised in interpreting this result because the actual numbers are small and the statistical power is limited.

Extracellular ATP and ATPgammaS suppress the proliferation of human periodontal ligament cells by different mechanisms

BACKGROUND

Periodontitis, similar to many other known inflammatory diseases, is thought to increase adenosine triphosphate (ATP) levels in extracellular spaces. Extracellular ATP acts on specific receptors to modulate the proliferation of various cell types. Platelet-rich plasma (PRP) contains high levels of ectonucleotidase activity capable of degrading ATP. The aim of this study was to investigate the effects of ATP on the proliferation of human periodontal ligament (PDL) cells and how these effects are altered by ectonucleotidases.

METHODS

PDL cells were derived from healthy young volunteers. ATP content and DNA synthesis were quantified by a bioluminescence and an enzyme-linked immunosorbent assay, respectively. CD39 and p21(WAF1/cip1) expression was analyzed by Western blot. Apoptosis was evaluated by caspase-3/7 activity, terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) activity, annexin-V-binding, and DNA fragmentation.

RESULTS

CD39 and ectonucleotidase-like activity were found in PDL cells and serum, respectively. Because less CD39 is expressed in freshly plated cells, both exogenous ATP and ATPgammaS, a slowly hydrolysable analog, inhibited cell proliferation under low serum conditions. ATP upregulated p21(WAF1/cip1), an inhibitor of cell-cycle progression, whereas ATPgammaS induced caspase-dependent apoptosis. Either upregulation of CD39 or added serum rescued cells from the cytostatic actions of exogenous ATP.

CONCLUSIONS

In PDL cells expressing low CD39 levels, both ATP and ATPgammaS inhibited proliferation but by different mechanisms. ATP-induced growth arrest suggests that periodontal tissue regeneration is often suppressed at the site of injury. Furthermore, added ectonucleotidases protected PDL cells from ATP's cytostatic actions, suggesting that ectonucleotidase-rich PRP augments the regenerative actions of its constituent growth factors by protecting against exogenous ATP at clinical sites.

The effect of different platelet-rich plasma concentrations on proliferation and differentiation of human periodontal ligament cells in vitro

OBJECTIVES

The use of platelets and platelet products has become increasingly popular clinically as a means of accelerating endosseous wound healing. It is likely that growth factors released by activated platelets at the site of injury play a role in periodontal regeneration by regulating cellular activity. The purpose of this study was to evaluate the biological effects of platelet-rich plasma (PRP) on human periodontal ligament cells (hPDLCs) in vitro.

MATERIALS AND METHODS

Primary cultures of hPDLCs were obtained from healthy premolars. PRP was isolated by two-step centrifugation. Two main growth factors present in the thrombin-activated PRP (platelet-derived growth factor [PDGF-AB] and transforming growth factor-beta1 [TGF-beta1]) were evaluated using ELISA assay. Activated PRP or the combination of recombined human TGF-beta1 (rhTGF-beta1) and PDGF-AB (rhPDGF-AB) were added to hPDLCs in different concentrations to assess cell proliferation and osteogenic differentiation.

RESULTS

PRP contained high levels of TGF-beta1 and PDGF-AB. Cell attachment, proliferation and ALP activity were enhanced by addition of PRP or rhTGF-beta1 and rhPDGF-AB combination to the cell cultures, while the stimulatory potency of PRP was much greater than the latter. These stimulatory effects presented in a dose-dependant manner, it seemed that PRP with 50~100 ng/ml TGF-beta1 was an ideal concentration.

CONCLUSIONS

PRP can enhance hPDLC adhesion, proliferation and induce the differentiation of hPDLC into mineralized tissue formation cell; thereby contribute to the main processes of periodontal tissue regeneration. For economical and biological reasons, PRP has more clinical beneficial than analogous growth factors.

Platelet-rich plasma/osteoblasts complex induces bone formation via osteoblastic differentiation following subcutaneous transplantation

BACKGROUND AND OBJECTIVE

Platelet-rich plasma (PRP) has been shown to enhance the maturation of bone grafts following local application and to have biological effects on osteoblasts in vitro. However, PRP is not applied by itself clinically as a result of its poor benefits in large bone defects. The present study was undertaken to develop a clinical alternative to autologous bone, by investigating the application of PRP in combination with osteoblastic cells and evaluating its effects after transplantation.

MATERIAL AND METHODS

PRP and platelet-poor plasma (PPP) were prepared from blood, obtained from ddY mice, by two centrifugation steps. MC3T3-E1 cells were labeled with fluorescent carbocyanine just before transplantation. The combination of labeled cells and PRP gel was subcutaneously transplanted into the back of severe combined immunodeficient (SCID) mice, and the transplants were evaluated radiographically and immunohistologically after 4 wk. The effects of PRP were assessed by alkaline phosphatase (ALP) staining and von Kossa staining, and the expression of bone-related markers was analyzed by reverse transcription-polymerase chain reaction before transplantation.

RESULTS

Before transplantation, PRP enhanced the expression of Osterix and bone sialoprotein mRNAs compared with PPP. Furthermore, PRP elevated ALP activity and induced the formation of mineralized nodules. After transplantation, the combination of labeled cells and PRP gel formed mineralized tissue, and the transplanted cells visualized in the tissue using fluorescence microscopy expressed osteocalcin and type I collagen.

CONCLUSION

These results suggest that the application of a PRP/osteoblasts complex has beneficial effects for transplanting engineered cells into bone defects through the promotion of osteoblastic differentiation.